Re: [Discuss-gnuradio] Question on tags - offsets

[Jeon]

Dear Anil,

Not every 64 items,but work() function is called if there are more than 64 items in the input stream (buffer).

Regards,

Jeon.

2015-06-19 11:51 GMT+09:00 Anil Kumar Yerrapragada <address@hidden>:

Hi, 

A quick question on tags. 

I'm coding a custom block in python and my forecast function is like so: 

def forecast(self, noutput_items, ninput_items_required):

        #setup size of input_items[i] for work call

        for i in range(len(ninput_items_required)):

            ninput_items_required[i] = 64

If my understanding is correct, every 64 items, the block's work function is called. 

Each time work is called, I want to add a tag to the first of the 64 elements that come in (the *value* of my tag is a list). So I used: 

lst = (1, 2, 3, 4) #example

        item_index = 0

        offset = self.nitems_written(0) + item_index

        key = pmt.string_to_symbol("example")

        value = pmt.to_pmt(lst)

        self.add_item_tag(0, offset, key, value)

This works. I can see the tag being added when I use a QT time sink. 

But when I add some print statements and check what I noticed is that tags are being added at indicies 0, 8192, 16384 etc. Basically multiples of 8192 which is the full length of the input buffer in0 = input_items[0].

Shouldn't self.nitems_written(0) be 64 each time? 

What I really want is tags being added at 0, 64, 128 etc. I'm sure I'm missing something pretty silly. 

Thanks

Anil

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